Sources of wastewater from various stages of tar deep processing

The work has finally been completed. The wastewater sources are mainly as follows: 1. In the tar pretreatment section: phenol-containing wastewater generated by super centrifuges; 2. In the tar distillation, washing and decomposition, and industrial naphthalene sections: phenol-containing wastewater resulting from the separation of light oil and phenol oil; 3. In the washing and decomposition section: sodium sulfate wastewater

Investigation report on the tar wastewater from a certain company: 160,000 tons of tar are processed annually. Analysis of the wastewater generated in the tar processing area shows that, based on the sources of this wastewater and the collection systems in place, the area can be divided into four zones: the industrial naphthalene section, the oil storage area, the phenolate production section, and the light oil tank area (the details of the wastewater situation are shown in the figure below). (1) The wastewater generated within the industrial naphthalene production area is collected in two underground wastewater tanks and one horizontal tank; the specific collection methods are as follows: ① The underground tank located next to the triple-blended oil feed tank is used to collect water from this tank, as well as water from the phenol oil tank and some surface wastewater in the vicinity ； The main pollutants are phenols, washing oils, naphthalene, alkalis, etc. ② The groundwater tank located next to the industrial naphthalene tower: it is used to collect the cooling water from the pumps, any leaked water, as well as engine oil and lubricants that have been washed away ； The main pollutants include phenols, naphthalene, washing oil, engine oil, etc ； ③ Horizontal tank: Responsible for collecting all the production wastewater from the industrial naphthalene process, and then sending this wastewater to the horizontal tank located in the oil storage area. Currently, according to the production schedule, approximately 100 tons of wastewater are sent to the oil removal machine per shift (an 8-hour shift) ； According to the monitoring report, the main pollutants in the wastewater are phenol (about 3000 mg/L), oil (about 15 g/L), etc. (2) Phenolate section (operating for 15 days per month): The wastewater generated during the production in the phenolate section mainly includes crude phenol distillation water (60 t/d), water from the crude phenol dehydration tank, as well as Na2CO3 waste liquid (2 t/d), water from the crude phenol washing tower (7 t/d), and purge steam water (10 t/d), among others. The phenolate section has two wastewater tanks; the pre-wastewater tank is used to collect Na2CO3 waste liquid, water from the crude phenol washing tower, etc. The amount of oil-removed wastewater sent away per shift is 18 tons. The wastewater contains high levels of phenol, color, and COD, while the oil content is low. The wastewater rear tank is responsible for collecting the water generated during the distillation of crude phenol and the water separated from the crude phenol dehydration tanks. The amount of oil-free wastewater discharged per shift is 20 tons; the main pollutants include phenol (about 2000 mg/L), sulfides (about 370 mg/L), COD (about 90,000 mg/L), ammonia nitrogen (about 300 mg/L), and oil (around 500 mg/L). (3) Light oil tank area: The light oil tank area is located behind the distillation tower area and consists of several horizontal tanks and oil storage vessels. There is an underground sump in this area, which primarily collects the water separated from the oil after the condensation of the light components from the evaporator (with a composition similar to that of the ammonia water in the recovery workshop), as well as water drained from the light oil tank, coolant water for the pumps, and any leaked oil or water. This wastewater tank delivers about 30 tons of wastewater to the oil removal machine per shift. The main pollutants in the wastewater are phenols, oils, COD, and ammonia nitrogen, all of which are present in high concentrations. (4) The wastewater generated from production in the workshops within the oil depot area is all collected in the wastewater system of that area. The oil tanks in the oil depot area used for storing finished oil, such as the washing oil tanks, de-arene oil tanks, and waste oil tanks, produce water that separates due to settling; this water is sent to a 70-ton horizontal tank located next to the super centrifuge for collection. The main pollutants in these wastewater streams are oils; the levels of phenols and ammonia nitrogen are low (the water discharged from the oil waste tanks contains a high amount of phenols due to the presence of oily substances). The volume of this wastewater is not large, around 20 tons per day ； The crude tar delivered from the first and second recovery processes must be dehydrated before it can be sent for distillation. The wastewater resulting from this dehydration process (with properties similar to the circulating ammonia water in the recovery plant) is collected in wastewater tanks No. 96 and 97 in the oil storage area, with a volume of about 50 tons per day ； The wastewater generated by the super centrifuge is sent to a horizontal tank; the volume of this wastewater is 10 tons per week, which is negligible (it belongs to the same category as recycled ammonia water) ； Next to the horizontal tank, there is a groundwater tank designed to collect the cooling water from the pumps in the oil storage area, surface wash water containing oil and sewage, as well as other types of leaked oil and wastewater; the volume of water collected is 50 tons per shift ； The oil removal machine receives about 300 tons of wastewater per shift; after oil removal via air flotation, the wastewater is sent to the ammonia intermediate tank in the second recovery workshop. The pollutant levels in the wastewater after oil removal are generally around 2000 mg/L for phenols ； COD 10,000～20,000 mg/L ； Ammonia nitrogen is around 400 mg/L ； Cyanide at around 100 mg/L. Figure 2.11 Wastewater conditions in the tar workshop (5) In addition to the wastewater generated during the production process, there are also other types of wastewater from the tar workshop that do not enter the wastewater treatment system; these waters flow directly into the refinery’s drainage pipes. The specific statistics are as follows: Tar distillation section: Heating water for the thousand-ton tar tank – 25 t/d; Water flow from the gas water seal – 8 t/d; Cooling water for pump heads – 15 t/d; Other types of water usage – 6 t/d. Total: 54 t/d. Industrial naphthalene section: Water flow from the gas water seal – 8 t/d; Cooling water for pump heads – 15 t/d; Steam for heating – 15 t/d. Total: 38 t/d. Phenolate section: Cooling water for mist eliminators and cooling towers – 20 t/d (based on 15 days of production per month); Other types of water usage – 5 t/d. Total: 25 t/d. Modified asphalt production section: Cooling water for chain conveyor systems – 60 t/d; Cooling water for mixer reducers – 4 t/d; Other types of water usage – 3 t/d. Total: 67 t/d. (6) Procedures for collecting and removing oil from wastewater in the tar processing plant: Based on the operations in the tar processing plant and considering practical conditions, the current procedures for centralized oil removal from wastewater are as follows: Morning shift: 04:00–12:00 – Collection of wastewater from oil storage tanks and light oil tanks. Afternoon shift: 12:00–20:00 – Collection of wastewater from the industrial naphthalene section and the phenolate section. Night shift: 20:00–04:00 – Collection of other types of wastewater generated during this period. Approximately 300 t of wastewater is processed per shift; thus, the amount of wastewater after oil removal in the tar processing plant is around 35–40 t/h. (7) The total amount of pollutants discharged in wastewater can be roughly calculated based on the average values of the monitoring results for various streams of wastewater from the coking company, as well as the volume of wastewater determined through investigations. The average amount of pollutants discharged from the tar production workshop is as follows: phenol: 82.2 kg/h ； Cyanide: 3.75 kg/h ； COD: 151.2kg/h ； Ammonia nitrogen: 16.1 kg/h Sulfides: 11.3 kg/h ； Oil: 202.6 kg/h. The wastewater from the tar workshop after oil removal is sent to the ammonia intermediate tank in the secondary recovery workshop. 2.4.3 Measures Taken and Evaluation of Water Pollution Control in the Tar Workshop To reduce the impact of wastewater discharged during production on the environment, the tar workshop has implemented the following measures for wastewater pollution control: (1) Groundwater tanks have been installed in each production section to collect various types of production wastewater as well as wastewater resulting from leaks. The wastewater collected in these tanks is pumped to the oil removal equipment in the workshop, and after oil removal, the wastewater is sent to the secondary recycling workshop. Every effort was made to minimize the impact of wastewater discharge on the environment ； (2) Since the various wastewater streams generated in the tar workshop generally have a high oil content, an FJL air flotation oil removal system was installed in the workshop to remove oil from these wastewaters. This not only reduces the oil content of the wastewaters sent to the recycling workshop but also allows the recovered oil to be reused as raw material for tar distillation, thereby improving resource utilization ； (3) In the tar workshop, most of the wastewater resulting from oil removal and sent to the secondary ammonia recovery intermediate tank consists of ammonia water, thereby improving the recycling rate of water ； (4) A horizontal tank was installed in the oil depot area as an intermediate tank for collecting wastewater and treating it to remove oil; the wastewater from various sources is first collected in this intermediate tank before being sent to the oil removal machine. The intermediate tank can effectively mitigate the impact caused by large fluctuations in the amount of wastewater generated in various processing stages, preventing the direct discharge of wastewater resulting from accidents ； However, the following problems still exist: (1) The water in the gas water seal, the steam from various production stages, and all wastewater from the modified asphalt stage are currently discharged directly outside. Although the pollutant content in this portion of wastewater is low, the volume is 184 t/d. Discharging it directly not only results in a waste of water resources but also has an impact on the environment. Its recycling should be considered ； (2) Since the types and concentrations of pollutants in different streams of wastewater vary greatly – for example, wastewater from the crude phenol stage contains high levels of phenol, while wastewater from oil tanks has high oil content – the current procedures established in the workshop for collecting and sending wastewater to oil removal units are based solely on production considerations. However, the composition of pollutants in the collected wastewater is closely related to the timing and volume of wastewater sent to the oil removal units from various collection tanks. By taking into account the specific conditions of each type of wastewater and the pollutants present, by arranging a more rational wastewater collection process, and by carrying out pre-treatment of these pollutants before centralized oil removal, it is possible to reduce the overall amount of pollutants emitted and improve the overall environmental quality.

The explanation on floor 3 is too detailed; learn from it*